1. Field of the Invention
The present invention relates to a luminaire to be used in interior lighting like offices to increase brightness sensation in the room without giving glare.
2. Related Art of the Invention
FIG. 17 shows a schematic diagram of three representative types of conventional indoor luminaire, and FIG. 18 shows the relation between the downward vertical angle from nadir and luminance in the conventional luminaire.
FIG. 17 (a) shows the so-called exposed type luminaire, which is designed to distribute light almost uniformly to the working surface, wall surface and ceiling, and the lamp is seen directly.
The luminance at 45 degrees to 85 degrees of the downward vertical angle from nadir (the direction of direct vision in ordinary sitting position) is about 8000 cd/m.sup.2 as shown in FIG. 18 (a). The downward projected area of the luminaire luminous element is about 0.035 m.sup.2.
FIG. 17 shows the so-called glare controlled type luminaire, in which a wedge-shaped lattice louver is attached to the lower surface of the luminaire in order to prevent glare by reflection on the CRT surface of VDTs (Visual Display Terminals) or the like.
Accordingly, as shown in FIG. 18, the light distribution of luminous intensity at the downward vertical angle of 60 degrees or more of the luminaire is strictly limited, and the luminance at the downward vertical angle of 60 to 85 degrees is 50 cd/m.sup.2 or less. The downward projected area of the luminous element is about 0.35 m.sup.2.
FIG. 17 (b) is intermediate of (a) and (c), and it is generally called the lower open type luminaire, and the lamp is seen directly when installed closely to the office worker, but the lamp is not seen directly when installed at a horizontal distance of about 15 m or more.
The luminance of this luminaire at the downward vertical angle of 60 to 85 degrees is about 1500 to 6000 cd/m.sup.2 as shown in FIG. 18, and the downward projected area of the luminous element is about 0.35 m.sup.2.
These lighting implements are used in ordinary offices, and other types include the lamp called downlight which is mainly used in shops, and the luminaire for small fluorescent lamps.
The downward projected area of the luminous element of these lighting implements is 0.0122 to 0.0177 m.sup.2 (the diameter is about 0.125 to 0.15 m).
In addition to these representative lighting implements used indoors, the luminaire generally called chandelier is known.
It is not intended to "illuminate something," but is to present a gorgeous atmosphere by giving sparkle and brilliance by combining small incandescent lamps of high luminarice and glass beads or the like.
Its luminous element comprises the lamps and glass beads, and the downward projected area of each light emitting unit is 0.001 m.sup.2 or less.
Accordingly, the apparent size at a distance of several meters is about 4.times.10.sup.-5 [sr], and the luminance is more than 20,000 [cd/m.sup.2 ].
However, in the exposed type luminaire shown in FIG. 17 (a), since the luminance at the downward vertical angle of 60 to 85 degrees to be seen directly in the ordinary sitting position is high, about 8000 cm/m.sup.2 as shown in FIG. 18, and glare may be felt when seen at the downward vertical angle in this range.
In the glare controlled luminaire in FIG. 17 (c), to prevent glare to the human eye or glare by reflection on the CRT surface, the luminance of the luminous element (direction of 60 to 85 degrees of perpendicular angle) seen in the ordinary sitting position is controlled under 50 cd/m.sup.2, and it is sometimes until whether the light is lit or not, and the office worker does not know from which direction the light is coming and feels uncomfortable, and moreover since there is no bright part on the ceiling, the entire room is gloomy, and the visual environment is dark.
In the lower open type luminaire in FIG. 17 (b), the luminance of the luminous element (60 to 85 degrees of perpendicular angle) of the luminaire seen in ordinary sitting position is about 1500 to 6000 cd/m.sup.2, and the lamp is seen directly at a close distance and the glare is significant.
At a long distance, to the contrary, since the lamp is shielded, glare is eliminated, but the room looks gloomy because there is no bright part of luminous element on the ceiling same as in the glare controlled type luminaire in FIG. 17 (c).
In the downlight, on the other hand, using incandescent lamps or small fluorescent lamps, the luminance in the downward vertical angle range of 60 to 90 degrees is about 2000 to 6000 cm/m.sup.2 and there is no glare in the downlight at a long distance from the observer, but the glare is felt from the downlight at a close distance.
Furthermore, the chandelier gives a gorgeous atmosphere by the diamond-likebrilliance and is free from gloomy feeling, but the absolute quantity of light is small, and enough illumination for visual work cannot be obtained.
Besides, the overall size of the chandelier is relatively large and it is suspended from the ceiling, and hence it may give a feeling of oppression or block the visual field when used in an office with a low ceiling of about 2.5 m.